The invention relates to a manual device for the determination of photometric data. More specifically, the invention relates to a manual device to measure photometric data, which includes a support surface to be placed onto a flat measuring surface and a measuring head movably mounted in a housing in an essentially straight line manner and parallel to the support surface, the measuring head being capable of movement between a rest position in which a measuring diaphragm serving to position the manual device on the measuring surface is visible to the user, and a working position in which it covers the measuring diaphragm, the measuring head further being mounted on a motor-driven measuring carriage movably located in the housing of the manual device, with a drive motor being fastened to said measuring carriage, and with a drive pulley actuated by the drive motor and equipped with a crank pin, said drive pulley engaging a slide guide mounted stationarily in the housing.
A manual top view densitometer for the graphical industry is known from EP No. 171 360 A2 and makes it possible with the measuring head extended, to completely rotate a filter wheel twice, while the drive pulley cooperating with the sliding guide travels over an angle of only about 90.degree.. The translation applied not only increases the rotating angle, but also enlarges the positioning error of the drive pulley, for which reason the known mechanical layout does not make it possible to carry out an accurate angular positioning of the filter wheel. The crank pin located at the drive pulley is permanently engaged in the slide guide, which has a specially adapted configuration.